Field of the Invention
The present invention relates to fire alarm systems for detecting presence of a fire and type of smoke from the scattered light caused by the smoke at the time of fire. More particularly, it relates to a fire alarm system which, in view of the fact that the scattering angle and the degree of polarization are different by types of smoke, is designed to be capable of more accurately judging a fire by varying the threshold for judging a fire based on the difference in the types of smoke.